In recent years, electronic equipment has been required to be smaller in size and more functional and operate at higher speed. In order to realize such requirements, electronic components such as semiconductor devices need to be highly densely mounted in equipment. In response to such a need, there have been developed a mounting structure in which a semiconductor chip including a non-packaged bare IC is directly mounted on a circuit board.
FIG. 6A shows a cross section of the conventional mounting structure including a semiconductor chip mounted on the circuit board. A mounting structure 200 comprises a semiconductor chip 1 and a circuit board 2. The semiconductor chip 1 includes a bare IC 11 and an interposer board 12 with the bare IC 11 mounted thereon. On a surface of the interposer board 12 opposite to the surface on which the bare IC 11 is mounted, solder balls 13 serving as terminal electrodes are formed. The solder balls 13 and lands (electrodes) 21 formed on the mounting surface of the circuit board 2 are bonded to each other with a solder 3, so that the semiconductor chip 1 is mounted on the circuit board 2. It should be noted that in FIG. 6A, only the bare IC 11 is shown not by a cross section but by a hollow rectangle representing the contour.
In such a conventional mounting structure, after a semiconductor device is secured to the circuit board by soldering such as reflow soldering, sealing of the soldered portion with resin (hereinafter referred to as “resin-sealing”) is generally performed for the purpose of ensuring the reliability of the mounting structure including an electronic component. Specifically, the resin-sealing is performed for the purpose of preventing a contact failure between the semiconductor device and the circuit board that may occur when the mounting structure undergoes repeated heat cycles or suffers an impact due to dropping etc.
To be concrete, as shown in FIG. 6A, in the space between the semiconductor chip 1 and the circuit board 2 where the electrodes formed thereon are bonded to each other with the solder 3, there is formed an electrically insulating sealing body 4 mainly composed of a thermosetting resin. Since the semiconductor chip 1 and the circuit board 2 are secured to each other with the sealing body 4, it is possible to prevent separation or cracks from occurring at the bonding portion formed of the solder 3, when a thermal or mechanical stress is externally applied to the mounting structure.
On the other hand, with the improvement in functionality and the increase in speed of operation of electronic equipment, the semiconductor device constituting the mounding structure tends to consume more power. For this reason, in addition to the need for highly dense mounting, there has been an increasing need for a mounting structure of an electronic component capable of excellent heat dissipation mounting, that is, capable of realizing an excellent heat dissipation performance.
In order to improve the heat dissipation performance of the mounting structure of an electronic component, in the conventional techniques, the amount of heat to be dissipated has been increased by attaching a heat dissipation board to the semiconductor device or electronic component that is required to be capable of dissipating heat, or alternatively by adding a modification to the configuration of the mounting structure (see, for example, Japanese Laid-Open Patent Publication No. Hei 4-155853, Japanese Laid-Open Patent Publication No. Hei 4-12556, and Japanese Laid-Open Patent Publication No. Hei 6-232294). However, attaching a heat dissipation board or adding a modification to the configuration has resulted in an increase of the volume of the mounting structure. This means that the electronic equipment incorporating such a mounting structure with an increased volume becomes large in size, which contradicts the need for reduction in size.
Under these circumstances, in order to improve the heat dissipation performance of the mounting structure of an electronic component, the utilization of the above-described sealing body has been considered. The sealing body allows heat generated in the semiconductor device or electronic component to be released therethrough to the housing of the electronic equipment or in the open air, enabling the amount of heat dissipated to be increased without resulting in an increase of the volume of the mounting structure.
The sealing body of the mounting structure has been improved in view of improvement in heat dissipation performance and prevention of cracks. FIG. 6B shows a partial cross-sectional view taken along the line VIB-IVB of the mounting structure 200 of FIG. 6A. The sealing body 4 is formed by mixing a filler 41 with a resin 40 mainly composed of a thermosetting resin. The filler 41 is made of an electrically insulating material having a comparatively good thermal conductive property. The filler 41 is mixed for the purpose of improving various properties of the sealing body 4, in particular, the thermal conductivity and the adhesive strength.
As discussed above, conventionally, the properties of the sealing body has been improved, and the thermal conductivity has been increased. However, if a large amount of the filler 41 is mixed with the sealing body 4 in order to obtain a sufficient heat dissipation performance in the mounting structure, the adhesion between the sealing body 4, and the semiconductor chip 1 and the circuit board 2 becomes insufficient, and the adhesive strength exerted by the sealing body 4 may be adversely reduced. For this reason, currently, the heat dissipation performance obtained by the conventional heat dissipation configuration utilizing the sealing body 4 is not sufficient enough to meet the needs for improving the functionality and increasing the speed of operation of electronic equipment.
The invention is made in order to solve the above conventional problems and intends to provide a mounting structure satisfying both conditions of adhesive strength and heat dissipation performance required for the sealing body.